Hydrogen has been attracting attention as a clean fuel, because its combustion does not generate carbon dioxide. However, industrial production of hydrogen has depended on fossil fuels, and therefore carbon dioxide is emitted in the production process of hydrogen. Thus, even if hydrogen is used as a fuel, exhaustion of fossil fuels and global warming due to carbon dioxide cannot be solved. Therefore, a great deal of attention has been drawn to a photocatalyst capable of splitting water using a natural energy such as sunlight to produce hydrogen.
Japanese Unexamined Patent Publication (Kohyo) No. 2010-519057 describes use of at least one nanoparticle as a photocatalyst for a variety of chemical reactions such as redox reaction and water splitting wherein the at least one nanoparticle comprises at least one metal/metal alloy region and at least one semiconductor region having an absorption onset in the visible (400-700 nm) to near infrared (NIR) range (0.7-3 μm), wherein the at least one semiconductor region is of Group III-VI and is selected from the group consisting of InSe, InTe, InS, GaSe, InGaSe, InSeS, and alloys thereof.
Japanese Unexamined Patent Publication (Kokai) No. 2010-046604 describes a photocatalyst using a compound A comprising a metal ion having a dn (0<n<10)-type electron configuration, an oxide ion (O2−), and an ion of at least one element B selected from the group consisting of H, Li, Na, K, Rb, Cs, Mg, Ca, Sr, rear earth elements, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Cu, Ag, Au, Zn, Cd, Al, Ga, In, C, Si, Ge, Sn, N, P, Sb, S, Se, Te, F, Cl, Br, and I (provided that when the element B is a metal element, the ion of the element B has an electron configuration other than the dn (0<n<10)-type electron configuration). Japanese Unexamined Patent Publication (Kokai) No. 2010-046604 further describes that hydrogen can be produced by contacting such a photocatalyst with a hydrogen-containing compound while irradiating light.